Technical Field
This invention relates to a sensor element and a sensor comprising this type of sensor element, where the sensor compounds (indicators) contained in the sensor element are protected against damaging or inactivating influences, such as highly reactive compounds. The invention further relates to the use of the sensor element and the sensor for determining an analyte in an environment which is aggressive for the indicator.
Discussion of Related Art
Sensor structures containing excitable sensor compounds (indicators) are generally known. The sensor principle is based on the fact that the indicators are first converted to an excited energy state by the supply of excitation energy. As the energy is released, e.g. in the form of light of a certain wavelength, the indicators switch to a lower energy level. The determination of an analyte in a sample is usually carried out by measuring the energy emitted by the indicators, which is sufficiently changed upon contact with an analyte to permit detection.
Different sensor types can be distinguished based on the form of their excitation and emission energy. The indicators of optical sensors can be excited, for example, by a supply of light, or chemical or electrical energy, although the emission always takes place in the form of light of a definite wavelength. In the case of purely optical sensors, the excitation and emission of the indicators takes place in the form of light of a specific excitation wavelength (v1) and emission (v2) wavelength. Optical sensors are used for example for the determination of oxygen, halide, and heavy metal ions, carbon dioxide (CO2) and of the pH value. The sensor principle may in this case be based on the measurement of luminescence quenching, the change in luminescence decay time, and/or the absorption of light waves.
At present, for the optical measurement of dissolved oxygen, sensors are used which are based on the property of certain luminescence indicators, whose luminescence of wavelength v2 is excited by light irradiation of a certain wavelength v1, and is dynamically quenched in the presence of oxygen, such that oxygen causes the radiationless deactivation of the excited state of the luminescence indicator.
Optical sensors are widely used for the reliable determination of an analyte in complex media, because the measurement methods used here are comparatively simple and require little equipment expense. However, conventional optical sensors have the disadvantage that the sensor elements do not provide adequate protection of the indicators they contain from destructive influences, and in particular from reactive compounds in the environment being analyzed. As a result, the service life of established sensor elements is especially limited when the indicators are exposed to conditions under which they are permanently or irreversibly inactivated.
In various applications, the medium to be analyzed contains, for example, compounds which destroy the indicators due to a chemical reaction. Thus, the problem with the current state of the technology is that the optical sensor elements currently available for determining molecular oxygen either cannot be used or only with a very limited service life if the medium to be analyzed, such as waste water or water from swimming pools, contains strong oxidants such as ozone, superoxide or hydroxyl radicals or chlorine or peroxide compounds used for disinfection, the diffusion of which to the indicators in the sensor element cannot be prevented, and contact leads to the oxidative inactivation of the indicators. Due to the lack of protection for the indicators, conventional sensor elements are either not suitable or only to a very limited degree under these conditions.
There is therefore a need for optical sensors for the luminescence detection of analytes in complex media, in which the luminescence indicators of the sensor elements are effectively protected against destructive or inactivating influences from the environment being analyzed.
The sensors referred to in CN 102109488 A are only multilayered electrochemical oxygen sensors, the indicators of which are protected by a noble metal-doped layer with a catalytic function, which is arranged between the medium and the indicator-bearing layer.
Optical sensors, the sensor elements of which are effectively protected by the indicator-bearing layer or layers against attack by reactive compounds, thus enabling the long-lasting determination of an analyte by means of luminescence measurement in a (chemical) environment that is aggressive for the indicators, are not known from the prior art, nor can they be derived from it.